In former railway grade crossing protection arrangements, it was conventional practice to detect motion of oncoming trains by continuously monitoring the track impedance and by sensing a change in the impedance. It will be appreciated that the reliability of the motion sensing and the accuracy of the time of arrival prediction are dependent upon a linear relationship between the track impedance and the distance to a train. That is, under certain conditions, the distance that a train is from the highway crossing is directly proportional to the impedance across the track rails. However, when a broken rail exists in the approach zone, the impedance at the crossing is proportional to the distance to a train only as far as the break. Thus, a train cannot be detected beyond the point of the broken rail. It has been found that when a partial break of several ohms resistance occurs, the presence of a train just beyond the point of fracture appears to be several thousand feet further away. Thus, the result of a partial as well as total break in the approach tracks can significantly reduce the amount of warning time given to motorists and pedestrians at the highway crossing. In order to avoid such a potentially dangerous situation, it is mandatory to detect any broken rail in the approach zones so that appropriate action can be taken to protect the lives and property of individuals. Presently, railroad crossing warning systems employ one of two techniques for detecting broken rails, namely, either a wrap-around circuit or a high level detector. The wrap-around circuit employs an audio frequency overlay (AFO) track circuit which extends along the entire length of the approach zones. In practice, the AFO wrap-around circuit functions to provide an initial train entrance into the approach zone and thereafter transfers the control of the highway crossing warning apparatus to the motion detector. That is, only after the presence of a train is recognized by the AFO circuit is the motion detector activated to measure the distance to the approaching train. Thus, the use of the AFO wrap-around track circuit insures the crossing warning time will not be shortened or reduced due to the occurrence of a broken rail in the approach zones. However, the additional hardware required to implement AFO train detection results in a significant increase in the overall cost of the highway crossing protection system. The high level detector arrangement employs a threshold detecting circuit incorporated with the motion sensing apparatus. In case a high resistance break in a rail occurs near the crossing area, the track impedance increases beyond the normal operating limits of the apparatus. Thus, the high impedance level is detected and the crossing warning devices are activated under such a broken rail condition. However, while the threshold detector provides some minimum amount of warning time, in some instances, there may be a significant reduction in the crossing warning time. Accordingly, such a proposal is not entirely satisfactory since the hazard of a broken rail is not completely eliminated.